This is Steven Salzberg's blog on genomics, pseudoscience, medical breakthroughs, higher education, and other topics, including skepticism about unscientific medical practices. Here's where I can say what I really think about abuses and distortions of science, wherever I see them.

Another dietary supplement to avoid: calcium

Dietary supplements and vitamins are a multi-billion dollar business, driven by heavy advertising and constant promises that supplements will somehow make you healthier. For most people, vitamins and other dietary supplements are useless, and when taken in large quantities they can even be harmful. (See my article, "The Top Six Vitamins You Should Not Take" for specifics.)

Now we can add another supplement to the list of those that you shouldn't take: calcium. Calcium supplements are often sold on the promise that they strengthen your bones or prevent osteoporosis. Given that calcium is a major component of our bones, it seems sensible to assume that extra calcium might help strengthen them.

What seems sensible, though, doesn't always turn out to be true. A large new study published recently in the Journal of the American Heart Association shows that taking supplemental calcium leads to an increased risk of heart disease, by increasing the calcification of your arteries. That's a bad outcome.

The new study, led by John J.B. Anderson of UNC Chapel Hill and Erin Michos at Johns Hopkins University, looked at changes in coronary artery calcification over a 10-year period in 2,742 adults. Calcification of the arteries is strongly associated with heart attacks and other life-threatening events; basically, a calcified artery is a dangerously unhealthy artery.

The study found some surprising results that seem at first to be contradictory: people who simply consumed the most calcium through their diet had a slightly lower risk of calcification of the arteries - about 27% lower than the group with the lowest amount of dietary calcium. However, people who took calcium supplements had a 22% higher risk of calcification.

"Little of the additional calcium provided by calcium supplements, however, is incorporated in bone by adults."

In other words, if you just take a pill of concentrated calcium, your body can't handle it, and some of it seems to end up in the linings of your arteries, where it makes them rigid and contributes to cardiovascular disease. So rather than strengthening your bones, supplemental calcium might "strengthen" your arteries, but in a bad way. As the study explains:

"Rather than promoting bone health, excess calcium from the diet and supplements is postulated to accrue in vascular tissues."